/Engine/Source/Editor/UnrealEd/Classes/Editor/UnrealEdEngine.h
Mark all selected actors and BSP models to be hidden upon editor startup, by setting their bHiddenEd flag to true, if it is not already. This directly modifies/dirties the relevant actors/BSP.
virtual void edactHideSelectedStartup ( [UWorld](API\Runtime\Engine\Engine\UWorld) * InWorld )